NEW YORK (Reuters Health) – Although serum zinc concentration increases in response to intake of a liquid zinc supplement in Senegalese children, this is not the case with zinc-fortified food, researchers report in an April 13th online paper in The American Journal of Clinical Nutrition.

“This conclusion,” Dr. Kenneth H. Brown told Reuters Health by email “does NOT mean that zinc fortification is not useful, just that we are not sure how best to measure the impact of zinc fortification programs objectively.”

Dr. Brown of the University of California, Davis and colleagues note that food fortification is considered to be an effective, low-cost approach for delivering micronutrients, including zinc. Studies have shown that the total amount of absorbed zinc can be increased by the approach.

Simple, low cost methods are needed to efficiently evaluate the effect. Plasma or serum zinc concentration responds in a dose-dependent manner after zinc supplementation. However, it is unclear whether it is a useful biomarker for use with food fortification.

“Additional information,” said Dr. Brown, “is needed to confirm the efficacy of zinc fortification of cereal flours for improving the zinc status of high-risk subgroups of the population, such as young children, and information is needed on the overall effectiveness of zinc fortification programs.”

To investigate further, the team studied 137 Senegalese children aged 9 to 17 months. They were randomized to receive iron-fortified cereal porridge and a liquid multivitamin supplement without zinc, the same porridge with a liquid multivitamin supplement containing 6 mg of zinc, or the same porridge with 6 mg of zinc added to it along with the zinc-free liquid multivitamin supplement.

After 15 days, plasma zinc concentration rose by 4.7 mcg/dL in the liquid supplementation with zinc group. It fell by 1 mcg/dL in children not given zinc and by 1.8 mcg/dL in the zinc-fortified porridge group. There was no significant difference in levels between the latter two groups.

“Serum zinc concentration,” continues Dr. Brown, “does not respond rapidly to zinc fortification, so it may not be a useful indicator of program impact, at least not in the short term.”

He added that other researchers have suggested “that the levels of zinc fortification for young children in the US may actually be too high, in relation to theoretical zinc requirements.”

Thus, Dr. Brown concluded, “the need for zinc interventions varies in different populations, and we need better tools to assess the beneficial (and potentially harmful) effects of such programs.”

Am J Clin Nutr 2011.